A pair of top US dressage riders involved in a positive drug test case have been given the green light to compete in the country’s national championships.

London 2012 Olympian Adrienne Lyle’s ride Horizon and leading young dressage rider Kaitlin Blythe’s mount Don Principe (pictured) both tested positive for banned substance ractopamine while competing at Wellington CDI in February this year.

The riders were provisionally suspended by the FEI for two months as of 6 April and the horses were suspended until the FEI tribunal makes a decision.

It is FEI policy to provisionally suspend horses for an initial period of two months regardless of the source or cause of the positive sample and cites horse welfare, and a fair and level playing field for the purposes of the policy.

However, the owners and riders sought relief from the suspension and the FEI lifted the riders’ temporary bans on 28 April after evidence showed a feed supplement given to the two horses had been contaminated.

The Court of Arbitration for Sport (CAS) also ruled that the horses’ temporary bans be lifted from 8 May.

“This is a temporary decision, which is made pending the resolution of the CAS arbitration,” a CAS spokesman told H&H.

“These interim decisions are not published by our tribunal but the final decision will be.

“Given the urgency, no hearing took place but the parties concerned were able to express their position in writing.”

A FEI spokesman added: “The FEI Tribunal maintained the provisional suspensions of the two horses on horse welfare grounds and in order to ensure a level playing field, however both athletes applied to the CAS in Lausanne for provisional measures to request the lifting of the suspensions of both horses so that they could compete at the US Dressage Festival of Champions (18-21 May).

“The CAS granted the provisional measures this week (8 May), but still have to rule on the merits of the case.”

Ractopamine is on the FEI’s banned substance list, meaning that it is deemed by the governing body to have “no legitimate use” in the competition horse at any time.

It is a medicated feed additive that is approved in the US for use in pigs, turkeys and cattle to improve weight gain and lean muscle, but is not approved for use in horses. The substance has also been outlawed altogether in 160 nations, including members of the European Union, Russia and China.

Both horses were being fed a nutritional supplement made by animal feed specialists Cargill prior to the positive tests.

Investigations by the company have found this product included trace amounts of ractopamine.

“Through our investigation, we identified that Progressive Nutrition Soothing Pink, a nutritional supplement used to prevent gastric upset, contained an ingredient that included trace amounts of ractopamine,” said a statement from the company.

“At this time, we have identified and isolated the ingredient that was the source of the contamination and we have completely stopped use of the ingredient in all products.

“Cargill shares a passion for equestrian sports and is proud to support these riders. We are disappointed this happened and are very sorry for the temporary uncertainty.

“We are pleased that Adrienne and Kaitlin will be back competing very soon and thank them for their patience and understanding as we’ve worked through this issue with them, and we continue to support them and the owners in their efforts to address the FEI’s handling of this matter.”

A statement on Adrienne’s Facebook page said they are “extremely pleased” with the outcome.

“We wish to express our deep gratitude to the United States Equestrian Federation [USEF] and its leadership,” it read.

“They have provided us the sort of commitment and support that shows that they truly stand for the membership.

“We know how deeply the USEF is committed to keeping our sport clean and free of drugs, and we applaud that effort.

“In supporting us here, the USEF showed that strict enforcement of anti-doping rules need not be inconsistent with basic principles of fairness.

“We also want to thank the people at Cargill for their efforts and support. To their credit, they have worked very closely with us to find out how our horses tested positive for a banned substance — even though they knew that this might result in a finding that one of their Progressive Nutrition products was the source.

“They devoted their resources to helping us find answers swiftly, and we are grateful to them.”

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